1. Field of the Invention
The present invention relates to a carbon wire heating object sealing heater and a fluid heating apparatus using the same heater and more particularly to a carbon wire heating object sealing heater having an excellent heating characteristic which allows it to be used preferably for semiconductor processing and a fluid heating apparatus using the same heater.
2. Description of the Related Art
Semiconductor manufacturing processing requires strict temperature control under a heat treatment environment for various kinds of heat treatment processes such as oxidation, diffusion and CVD processing. Further, heating means in the heat treatment process absolutely needs to be non-generation source of a substance which deteriorates semiconductor performance such as impure metal. For the reason, a heater in which the outside of its heating element composed of tungsten and the like is covered with quartz glass has been often used.
If the quartz glass for covering the heating element composed of tungsten and the like happens to be damaged when the heater is used, for example, in a semiconductor manufacturing process field, atmosphere, cleaning fluid, grind fluid and the like are contaminated with the metal, so that wafers are also further contaminated. Even if the quartz glass pipe is not damaged, there exists such a problem that the metallic contamination may be generated from the heating element through the quartz glass.
From viewpoints for preventing the metallic contamination with impure metal, the inventors have proposed a carbon wire heating element sealing heater which can be used as a semiconductor manufacturing heater, which is more advantageous than the metallic heating element (Japanese Patent Application Laid-Open No. 2000-21890).
This carbon wire (heating element) is manufactured by knitting plural bundles, each bundle being composed of ultra fine carbon fibers. Its heating capacity is smaller and its temperature rising/declining characteristic is more excellent than a conventional metallic heating element and its high-temperature durability is excellent under non-oxidizing atmosphere. Because this carbon wire is manufactured by knitting plural bundles each composed of fine carbon fibers, it has more excellent flexibility than a heating element composed of bare carbon material and such an advantage that it can be processed easily into various configuration or shape as a semiconductor manufacturing heater.
In recent years, particularly in semiconductor manufacturing industrial filed, the diameter of the wafer has been increased more and more for large capacity integration of the semiconductor circuit and improvement of yield rate for reduction of cost has been demanded more strongly. To meet such demands, more strict temperature control than before has been demanded. For the reason, a heater with less heating unevenness so as to heat a treatment furnace and the like to a desired condition has been demanded.
Although this carbon wire heating element sealing heater is very excellent in views of prevention of impure metal pollution as described above, generation of black spots on an inner face of an element pipe (quartz glass pipe) in which the carbon wire heating element was sealed was noticed when that heater was used.
Particularly in a carbon wire heating element sealing heater having a U shaped side view, having a straight heating portion and provided with terminal portions on both ends of the same straight portion through each bent portion, generation of these black spots was noticed.
Generation of the black spots on the inner face of the element pipe (quartz glass pipe) in which the carbon wire heating element is sealed is not favorable because it blocks and shields from radiation heat thereby causing unevenness in heating.
Accordingly, the inventors of the present invention have noticed that generation of the black spots occurs under influences of absorption water quantity of the carbon wire in which the element pipe (quartz glass pipe) is sealed in and the inside diameter of the element pipe (quartz glass pipe) as a result of accumulated researches on the cause thereof and then, reached the present invention.
As shown in FIGS. 27A and 27B, the terminal portion of the aforementioned carbon wire heating element sealing heater comprises a glass pipe 421, wire carbon materials 423 accommodated within this glass pipe 421 in a compressed state, a carbon wire heating element 422 accommodated in the glass pipe 421 and nipped by the wire carbon materials 423, and a power supply connecting wire 424 accommodated within the glass pipe 421 and nipped by the wire carbon materials 423. A quartz glass member 425 constituting a heater main body is connected to an opening end portion 421a of the glass pipe 421 and the carbon wire heating element 422 is introduced out of the opening end portion 421a. This opening end portion 421a is slightly constricted in order to prevent internally loaded substance such as the carbon wire heating element 422 and the wire carbon material 423 from jumping out. On the other hand, the other opening end portion (not shown) of the glass pipe 421 is closed with other glass member with the connecting wire 424 introduced out thereof.
Such a structure connects the carbon wire heating element 422 with the power supply connecting wire 24 electrically through the wire carbon materials 423.
Conventionally, when the wire carbon materials 423 were accommodated in the terminal portion (glass pipe 421) in a compressed state, the wire carbon materials 423 were loaded in the glass pipe 421 by batch. For the reason, it sometimes comes that as shown in FIG. 27B, an end portion of the carbon wire heating element 422 is deflected toward a wall side of the glass pipe 421. As a result, as shown in FIG. 27A, a periphery of an opening end portion 421a may make contact with the carbon wire heating element 422. If the carbon wire heating element 422 and the glass pipe 421 make a direct contact with each other (because pressed), reaction between carbon (C) and quartz (SiO2) progresses at a contact point, so that breaking of wire is likely to occur at that point.
As regards the shape of the heater terminal portion, an L-shaped terminal portion as shown in FIG. 28 is also used. In this terminal portion also, the wire carbon materials 423 are loaded on a side 426a of the glass pipe 426 by batch so as to fix the carbon wire heating element 422 and then, the carbon wire heating element 422 is introduced to the other side 426b of the glass pipe 426. In the meantime, the heater main body is formed ahead of the other side 426b. 
If the carbon wire heating element 422 is bent at this terminal portion, the wire carbon materials 423 are swollen inside the bent portion of the L-shaped glass pipe 426 as shown in FIG. 28 so that the carbon wire heating element 422 is pressed against the inner wall of the glass pipe 426. As a result, the carbon wire heating element 422 makes a contact with the wall face of the glass pipe 426, so that reaction between carbon (C) and quartz (SiO2) progresses at this contact point, there by likely generating breaking of wire, which is a technical problem to be solved.
As described above, more strict temperature adjustment control has been demanded in the semiconductor manufacturing field. For this purpose, a heater capable of heating a treatment furnace and the like to a desired state or a heater having directivity in radiation heat has been demanded. Particularly, in a heater for heating the treatment furnace from its lateral direction, appearance of a heater having increased radiation heat in the direction of the vertical plane (lateral direction) has been demanded. For example, if as shown in FIG. 29A, the aforementioned rod-like heater 470 is erected vertically, radiation heat in the direction of the vertical plane is increased.
However, because only a heating element 471 is provided, a region in which radiation heat is transmitted is small. Thus, to increase the radiation heat transmission region, it is necessary to provide with plural rod-like heaters adjacent the aforementioned rod-like heater 470. In this case, a quantity of connecting terminals 472 corresponding to the number of the rod-like heaters is required, thereby leading to increase of cost, which is a technical problem to be solved.
By forming a heating element 476 of a plate-like heater 475 meanderingly as shown in FIG. 29B, the region in which the radiation heat is transmitted in the direction of the vertical plane can be expanded. Further, in this case, the quantity of the connecting terminals 472 is not increased so much as the case of the rod-like heater 470. However, because the heating element 476 meandering vertically is formed with a predetermined gap t, there is a limit in increasing the radiation heat in the direction of the vertical plane.
As described above, the carbon wire heating element sealing heater is very excellent in views of prevention of impure metal pollution. The inventors of the present invention considered other applications thereof in the semiconductor manufacturing field. As a result, they have noticed that the technology can be applied to a fluid heating apparatus and reached the present invention.